Surgeons often need to be able to look at both pre-operative data, such as computed tomography (“CT”) scans and magnetic resonance imaging (“MRI”) scans, as well as intra operative data, such as two dimensional (“2D”) ultrasound or three dimensional (“3D”) ultrasound while they are in the operating room. Normally, doctors view the CT scans and ultrasound on separate displays and must use their imaginations in order to correlate the information in the two images. This is a difficult spatial task for the surgeons to accomplish. Further, when a target anatomical site is located within soft tissue, the pre-operative data is out of date with respect its pre-operative form because of the movement, compression and reorientation of the soft tissue and, therefore, it is difficult or impossible for the surgeon to appropriately utilize the pre-operative data during the operation.
Previous systems have attempted to aid the surgeon using computer vision registration techniques. Example systems are described in, among other papers, Aylward et al., Analysis of the Parameter Space of a Metric for Registering 3D Vascular Images, in W. Niessen and M. Viergever (Eds.), MEDICAL IMAGE COMPUTING AND COMPUTER-ASSISTED INTERVENTION—MICCAI 2001, pp. 932-939; and Aylward et al, Intra-Operative 3D Ultrasound Augmentation, Proceedings of the IEEE International Symposium on Biomedical Imaging, Washington, D.C., July 2002. The problem with these systems however is the massive computational strain required by the registration techniques.